A fundamental study of tethered polymer chains in gel systems

Abstract

Two types of tethered polymers in the gel system were studied in this work. One involved polymer Chains grafted on the gel surface, while the other Consisted of the gel itself where mesh chains were tethered on each other through their chain ends. ^ Surface-tethered polymer chains were studied both theoretically and experimentally with the consideration of their application as adhesion promoters for the hydrogel mucoadhesion. On the theoretical side, the mucous layer was modeled as a highly-swollen gel, and the single-chain mean-field theory was used to examine the function of tethered polymers in the gel/gel adhesion. It was shown that the gel/gel adhesion Could be controlled by specifically designed tethered polymer layers. The effects of the following factors on the gel/gel adhesion had been studied: the polymer/gel interaction, the surface coverage of tethered polymers, and the copolymer compositions. On the experimental side, the interaction between mucins and tethered poly(ethylene glycol) (PEG) chains had been studied by adsorption experiments and direct surface force measurements, using surface plasmon resonance spectroscopy and surface force apparatus, respectively. The results suggested that the mucin/PEG interaction depended on the pH values of the buffer solution. In lower pH conditions, the binding between mucins and PEG chains was found to be stronger. ^ The single-chain mean-field theory was used to develop a new polymer gel theory, which took the mesh chains or star polymers as the characteristic units of polymer gels. Predictions based on the new theory were compared with the experimental data as well as the predictions of Flory theory. The effect of the preparation conditions on the relaxed state of gels was discussed. The ability of the new theory to describe gels of complex polymer structures was tested. ^